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poureJ out into the spaces between the teeth. The comparison of 

 the teeth of a leech to the teeth of a circular saw fails , be- 

 cause the points of the denticules hardly projecting if atall,can 

 not be used as the teeth of a saw. 



I believe therefore that the sharp edges of the cuticulae are 

 the cutting instruments, whereas the teeth only serve to support 

 them. Leuckart is of an other opinion. He thinks that the cuticula 

 is too feeble and that it gives way when the jaw is in function; 

 the teeth being for a greater part uncovered , form a real saw. 

 Against this explanation stands the fact , that Aulastoraum gulo , 

 having the largest teeth , can only wound the skin of frogs 

 difficultly, whilst Hirudo does it easily enough. 



It is noteworthy , that though the jaws of Limnatis nilotica 

 are formed quite in the same way as those of Hirudo, here 

 the teeth are absent; the aniraal can apparently use very well 

 its jaws without teeth. 



If we make a series of sections through the jaw, we can see, 

 that the cuticula on the place , where a tooth is found , is less 

 developed , than were there is noue , the tooth being so to say enclo- 

 sed in an hole of the cuticula. The circumstance , that the cuti- 

 cula surrounds the tooth on all sides, with exbeption of the 

 points , makes it difficult to form a good idea of the genese of 

 the teeth. If the teeth were covered by an epithelium, as Vogt 

 and Jung describe it, which is not the case, we could imagine them 

 to be a product of the epithelium, but as things stand now, 

 embryological investigation only can contribute to enlighten the 

 origin of the teeth. 



It is almost beyond doubt that the unicellular ■ — the prosto- 

 mial as well as the salivary — glands are the source of the sub- 

 stance which prevents the clotting of the blood and the conglu- 

 tination of the bloodplates. 



As to the nature of this substance Haycraft found that it is 

 not an enzyme , since its activity is not destroyed by boiling , 

 that it does not interfere with the clotting of milk under the 



